Actuator mechanism for power couplers



Sept. 14, 1954 E. E. wEMP AcTuAToR MEcHANIsM FOR POWER coUPLERs' *I sheets-sheet 1 Fle'd Jan. 4, 1951 Sept. .14, 1954 2,689,030

E. E. WEMP ACTUATOR MECHANISM FOR POWER COUPLERS Filed Jan. 4, 1951 7 Sheets-Sheet 4 I7 l [is /36 /SS 7J 53 98 U u l 1 Pci?. 6.

INVEN TOR. Ernes .E Wem/0 Sept. 14, 1954 E. E. WEMP ACTUATOR MECHANISM FOR POWER COUPLERS Filed Jan. 4, 1951 7 Sheets-Sheet 6 INVENTOR.

Ernes E #Mem/0. @WWMJW Sept. 14, 1954 E, E, WEMP 2,689,030

ACTUATOR MECHANISM FOR POWER COUPLERS Filed Jan. 4, 1951 7 Sheets-Sheet 7 nes E. Wem/o Patented Sept. 14, 1954 ACTU'IOR MECHANISM FORI.y COUPLER'S ErnestiE.Wemp, Detroit, Mich., assignor o'fi''v'e percent to Eleanor M; Wemp, Los Angeles,. Calif., five percent to Leah K. Smith,-ive:per cent to ClydeJ. Smith, andtwenty per cent' to Lila A.y Wemp, allvof Detroit, Mich.;` William ONeilvl'y K ronner and Lila A. Wemp; executorsv of'sa'id Ernest- E. Wemp, deceased Application January 4, 1951, Serial-No.12'0430# This vinventionrelates to improvements in automatic. transmissions fory automotive vehiclesl and especiallyY transmissions for passenger vehicles.

The general objectsof theinvention are to provide an improved automatic transmission with a. positive and. sure. actionl and. embodying a-.relativelysimplied construction so that it can be manufacturedY at a relatively low` cost and thus used on automotive vehicleswithout materially increasing the'cost thereof.v Moreover,

the invention aims tor provide a transmission of such a.- construction asto require a.- minimum of service in the. field anda transmission which, if it needs service, visnot soy complicated` or special.- ized .butwhatmost wellequipped service garages canservicethe same` In. this connection,` it may be stated that some automatictransmissions are quite complicated resulting in service diiculties.

The inventionviurther aims to provide a` trans mission ofthe type having. alow. speedrange and a.- high speedv range andwhich embodies ahydraulictorqueconverter for transmitting-` torque in the low speed range and a clutch for transmitting.A the. torque vin. the. highspeed. range.-y In conjunction with` this, is-gearingan'd. a. power coupler. The power `coupler is automatically-actuatedV in. accordance: with AspeedA andtorque conditions for causing the condition: ofthe transmission to change toand. from]4 the low speed range and. the high.4 speed. range.- In.- the low speed. range the torque.. is; transmitted.l through the. hydraulic torque converter. and. through the gearing, aseiectedby the. dentalfcoupling ofvthe powery coupler. In thehigh speed range,l torque is. transmitted by the. clutchv andthe hydraulic torque converter andfgearing transmitno torque dueto the releaseof. dental yengagement by the power. coupler. Thepower coupleris. one. which is.- arranged. to engage.- andP disengage a dental couplingwhile the parts, `which are brought into and .out yof',dentallengagement. are under torque load; that is to saythey are both being positively driven by the enginearrd/or the movingl vehicle.

These andother objectstwill'be better. appreciated'. as the following, detailed description is considered' in conjunction with the accompanying drawings which show a transmission construction in accordancewith the invention..

Fig. lis a. general cross sectionalview illustratingthe torque converter; the transmission gearing andthe clutch.

Fig. 2 is an enlarged" View in.l cross section showing the. torque converter 'andclutch Fig, 3"is..a detailed vi'ew illustratinggthev flexible drive for'thepressure plate-ofthe clutch.

Fig. i.isanrenlarged crossisectional view taken substantially online lm-41.V of Fig. 1 showingl the anti-creep brake.

Fig. 5 isfaviewfwith parts cut away and parts in section showing someV ofA the operating mechanismwithin the range change section of the transmission.-`

Fig.y 6is a sectional view taken through the range change section substantially on line 6--6 of Fig. 5 showing some of the gearing, the-coupler actuator, and the control valve block.

Fig. '7y is a detailed-view with somepartsgin cross section showing the actuating. mechanism for the power coupler.

Fig.; 8` is a viewillustratingthe power coupler and the geary membersassociated therewith.

Fig. 9 isaview taken'on line 9--9 of Fig.v 8 illustrating blocker structure for the-coupler.

Fig. 10 is a viewshowing adevelopment-ofi the teeth` on. the coupler.

Figla is a view similar tollig. l-showing the parts in-blocked position.

Fig.. 10-bis' a. view similar to Fig). 10 showing Ithe partsinengaged position. i

The transmission as` shown in Fig. 1L has a housing section I: for a torque converter,v amintermediate housing 2l for gearing of the range change section, anda-n end housing member 3. The crank-.shaft ofQan. er1-gine is shown at `5l lIt is drivingly connected with the impeller or driving member of arhydraulicto-rqueconverter,generally shown at 6, having aforward plate T and a rear wall 8 providednwith varies-9*. The rear wall 8 constitutesA a-part of thetoruschamber and the rear wall hasa projectinghub portioni.

rThe front plate!! 4is formed `to-provide .a cylinder for receivingthe piston portion offa. clutch' pressure plate lf2., the dei-"ined cylinder spacerbeing shown at i3. The pressureplate is drivingly conneoted to theengine as by means of yiiexible straps Ill-(Fig. 3) so ythat the pressure plate may shift axially for the purpose/ofv engagement and dis'- engagement ofa clutch. A clutch driven disc I5 has yits hub drivingly connected to a clutch shaft i 6. This clutch shaftfhas itsforwa'rd 'end `piloted as at I'iin the pressure plate l2 and itexten'ds through the transmission'.l an'dhas' ai iinal drive member i8 at itsrear en'dwhichv may beT one of the' members `of a universal. joint' coupling.' Al

. 3 or blades 22 and this member has its hub 23 drivingly mounted on a sleeve 24. This sleeve projects into the transmission housing 2 and is journalled in a' bearing 25, there being also a.

bearing 26 between the sleeve and the clutch shaft.

means or overrunningl clutch arrangement may` It permits the stator to rotate in one direction only (forward) but it` be ofthe sprag type.

cannot operate in the opposite direction (back-y ward) as the sleeve 30 is fixed from the standpoint that it is not rotatable.

There is a partition between the vhousing sections I and 2 constituted by a plate 35 vand a plate 31 which cooperate to provide a pump chamber. The pump is generally shown at 35. Within this chamber is a rotary type of pump having an outer member 38 and an 'inner member 39 and the inner member is keyed or` splined to the sleeve I as shown at 4|). Thus it -will be seen that this pump, conveniently called the front pump is driven directly by the engine. This pump has a suitabley pressure relief valve as shown at This type of torque converter is known to those skilled in the art. As the engine operates hydraulic medium, which may hereafter be termed oil, is pumped into the torus chamber by the pump and circulated therethrough and the impeller 8 drives the turbine 2| and torque is transmitted by the sleeve 24. At low speeds and at high torque the stator tends to rotate reversely which it cannot do because it is held by the one way drive coupling and the sleeve 30. The stator vanes so change the velocity angle of the oil that there is a torque conversion in that the engine operates at a higher R. P. M. than the sleeve 24 and a higher torque is transmitted'to the sleeve 30 since torque or speed vare reciprocal.` However, as the speed increases and the speed of rotation of the turbine approaches that of the impeller the reaction on the statorV blades diminishes and finally the stator merely idles and rotates in the direction of rotation of the impeller and turbine and performs no further function in changing the direction of the velocity flow of the oil. When this condition exists the impeller and turbine act essentially as a fluid coupling and are rotating without torque conversion and substantially at the same speed of rotation less that which is unavoidably present in a hydraulic coupling of this type.

In the range change section of the transmission is a gear 45 which may be integral with the sleeve 24. A gear 4S is ljournalled on the clutch ,l shaft I6 and a gear 41 also journalled on the shaft I6. There is a countershaft 48 with a gear cluster journalled thereon including a gear the teeth of which mesh with those of gear 45, a gear 5|, the teeth of which mesh with those of gear 46 and a reverse gear 52. The teeth of the reverse gear 5 2 (Fig. 6) mesh with the teeth of an idler gear 53 and the teeth of the idler gear mesh with those of gearv 41.

The gears 46 and 41, are spaced apart and between them lies a power coupler generally illustrated at 55. The gear :it` is provided with a set of internal teeth 56 for dental engagement The stator of the torque converter has a wall 21 with vanes or blades 28. The stator is mounted on a fixed sleeve 30 through the means` 4 with teeth 51 on the coupler. The gear 41 is provided with a set of internal teeth 58 for dental engagement with a set of teeth 59 on the coupler. The body or hub of the Acoupler `lill is slidably splined to the clutch shaft as indicated. As afore- 1 said, the clutch shaft extends out through the rear of the transmission and it is carried by a suitable bearing E2.

Before proceeding with further description the general operation may be referred to. In the low range, the coupler 55 is shifted to the left and f coupled with the gear 45. Accordingly, with the clutch disengaged the torque converter functions to transmit torque to the turbine thence to the sleeve 24 and gear 45. i This torque is transmitted through the gears 5S and 5| to the gear 45, thence to the coupler and to the clutch shaft. The torque converter may function to transmit torque starting from a very low speed ratio between the engine and the shaft I3 and al higher torque ratio and when conditions are such that the stator ceases to function as such and begins to idle; lthe torque is then transmitted through the fixed reduction provided by the gear train. At this time the gear train determines the relative speed and torque ratio except'for the unavoidable slip in the hydraulic convertery which is functioning at the time as a fluid coupling. Following this the clutch comprising parts I2, |5 and 23 is to be engaged and after engagement the torque is then transmitted directly to the 'shaft It and at this time the coupler 55 is disengaged from the gear 4'6. Also at this time, the turbine 2|, the sleeve 24, the gears 45 and 45, and the gear cluster, merely rotate in an idling fashion' in the sense that no torque is transmittedtherethrough except that necessary to overcome what little friC- i tion is present. When the coupler 55 is shifted to.

the right as Fig. 1 is viewed, to engage the teeth 58 and 59, the shaft IB is driven-in the reverse direction for theV purpose ofibacking up the vehicle. Inthis case the torque is transmitted through the converter and theV clutch is diseneased. f f

The power coupler is of the type shown in Pat. No. Re. 22,161 of May 28, 1946. and in Pat.`No. 2,441,174 of May 11,1948, andprobably needs only a general disclosure herein. The coupler member Eil, which is splined to the shaft Hi, has a flange 82 with apertures 53 therein. The coupler is shifted by shifting means applied to the iiange as will presently be seen. Two ring members 64 and E5 are arranged to receive pins 61 which pass through the apertures with clearance. Conveniently there are f threeV apertures in the Iiange and three pins. The ring member `|54 has a conical face 63 for frictionally engaging a conical face 69 on an-extension of the gear 46, while the ring 65 has a conical face 19 for engaging the conical face 1| of an extension onthe gear 41. There are springs `13 fastened to the coupler and arranged to engageeach vpinto maintain a frictional relationship. Each pin has lfore the coupler, are rotating faster than the gear 46. When the coupler is shiftedy to the left for the above purpose, the blocker rassembly, i. e. the rings 64' and 65. and'pins, 51, is

shifted tothe 1eft by vthe ati'onof` the` Springs f "I3 andthe faces, 68 and l|59? frictionally engage leach other. The relative motion reaction due 'to the .slower running gear 46 rocks the blocker .assembly relative to the coupler and the shoul- :ders 16 abut the shoulders 'I4 and thus blocks Imovement of the coupler. This position is shown in Fig. a. The relative motion reaction as indicated by the arrow R urges the blocker assembly to the kright as Fig. 10a is viewed relative to the coupler 60 and therefore shoulders 16 engage shoulders 14 and further movement of the coupler and its ange 62 toward the gear 46 is arrested. Thus the teeth 56 and5'l are held from engaging each other. However, when the gear 46 and the shaft |-6 approachY synchronization and particularly when the gear 4.6, tends to overrun the shaft I6 the relative motion reaction .reverses and the blocker assembly is shifted rotatably relative to the coupler to move the `shoulders 14 out of blocking position relative to shoulders 16 and then the coupler may continue its movement to the left to dentally engage the teeth 56 and 51 as shown in Fig. 10b. The same general action occurs in dentally engaging the teeth `58 and 59 for establishing reverse drive.

The teeth 56 and 51 are helically disposed as shown in Fig. 10` so that normally when torque is transmitted therethrough from the engine to the shaft |6, the angle of the teeth tend to hold he teeth in engagement with each other. On reversal of torque, however, that is, when torque is delivered from the shaft I6 and into the gear train, the inclined or helical teeth tend to reject the coupler or, in other words, tends to shift the teeth out of dental engagement. This tendency will not cause disengagement, however, in normal operation. In Fig. 9 a pin S'I is shown centered in the aperture 63 and the dotted line position thereof illustrates a blocking position, the pin having moved from a center as illustrated at 80 to a center 8|. Also, it will be seen how the helical teeth 59 on the coupler are removed at locations in order to accommodate the springs 13. Thus, the teeth 51 .and 59 are disposed in segmental groups but there are, of

adequate dental connection with the teeth on the gears.

There is another pump y02 for hydraulic medium which is driven by the shaft I6. This pump is shown as being located in the housing section 3 and it has a housing 83with a pump member 04 and a pump member 85 which is drivingly connected with the shaft I6. The pump has. a suitable pressure relief valve shown at 86. This may be termed the rear pumps The transmissionv case is provided with a bottom closure or pan 81 which constitutes a sump for the oil and the two pumps have a common inlet conduit or passageway 88 (Fig. 6) communicating into the sump. There is a screen 89 in the sump into which the inlet communicates. The screen is covered by a downwardly opening shell 98 to prevent oil surge. The-lower end of the shell is spaced from the bottom of the pan so that oil may freely enter. The screen is held in place by au spring 99 which seats on the bottom of the pan.81.

There is an anti-creep brake applicable to a torque transmitting member for restraining the vehicle against creeping actionwhen the engine is idling. This takes thefform of a brake member or disc 90 splinedor otherwise attached to the sleeve 2,4- and abrakefbandtl. Thestrucrto the right.

6 -tu'rel is: shown in Fig; 4. Each end kof the. brake band ,is 4provided with an end piece or @ear 9,2 and 93 and there are two oppositely acting springs v94 and 95 backed up by spring seats 96 and 9.1 which tendA normally to wrap the brake band on the disc. Heads |00. and |0| mounted on rods |02 and |03 transmit the thrust of the springs through struts |04 and |05 which engage .the end pieces or earsy 92` and 93. The rods |02 and |03 are bifurcated, each for receiving one end v|06 and |01 of bell cranks p-ivotedas at |08 and |09 and each having an arm H10 and I. A piston I I2 in a cylinder 3, to which oil under pressure may be vpumped through conduit ||4, has a projecting part ||5 for engaging the arms ||0 and as indicated. If oil under pressure is introduced into the cylinder the piston moves upwardly ras Fig. 4 'is viewed, the bell cranks are swung on their pivots and the springs are compressed and the load thereby relieved from the brake band to release the brake. If the cylinder is vented or opened to an exhaust the springs expand and theA brake is applied. Each spring seat has a cylinder formed therein as shown at |20 and `|2| and each rod has a piston mounted thereon and positioned in these cylinders as shown at |22 and |23. The springs can only be compressed to the point where the rods abut adjustable stops |24 and |25.

This anti-creepbrake arrangement is connected into the hydraulic service brake system of the vehicle. Diagrammatically illustrated in Fig. 4 isa brake pedal |26 of the vehicle which operates a piston in the master cylinder |21 of the hydraulic system and conduits illustrated convey the medium to actuating. units |:28 for each of the four wheels |29- of the vehicle. Leading from the master cylinder of the brake system is the conduit |30 which has branches |3| and. |32 and which respectively connect into-the cylinders |20 and |2 Therefore, when the brakes of the vehicle are applied, braking fluid is introduced into the cylinders and the pistons |22 and |23 shifted so as to compress` the springs 94 and 95 to release the brake'. Thel detailed manner of this operation andr the functions thereof will be later considered.

The power coupler is controlled both manually and automatically and the means for controlling it is shown in Figs. 5, 6 and 7 as well as in other figures. There is a lever |35 mounted on a control shaft |36 which has an operator or shoe |31 for engaging the flange of theV coupler. On the outside of the transmission case theshaft |36 is provided with an operating lever |38 to be connected by means not shown to suitable operating means convenient to theoperator. The operator` may shift the lever |38 to one of three positions. One position being forward, one being `neutral and the other reverse. The neutral position is shown in Fig. 7 where the coupler |30A is out of dental engagement with both gears 43 and 41. At this time a` detent |40 pressed by a spring |41 engages in a notch |42. On each side of this notch the lever has a cam surface as indicated at |43 and |44 with an abutment or limit stop at each end thereof as at |45 and |46. To shift the coupler manually into engagement with the gear 4-1 for reverse operation thelever |35 is rocked clock-- wise as Fig. 7 is viewed andthe coupler is-shifted The detent is forced out of the notch |42 and when the coupler engagesthe gear 41thelimit stop |46'engages'the detent |40. The cam |44' is so shaped that. when the detent, is,-

pressed-againstit theregisa tendency torockthe;

7 lever'4 |35 clockwise thus Ward. dental engagement with the gear 41. Disengagement of the coupler from the gear 41 may be effectedV by the reverse action shifting the i lever |35 'back to the position shown in Fig. 1.

The lever |35 is acted upon automatically by a power coupler servo in the form of ra cylinder |50 with a piston |5| therein mounted on a rod` |52. A coil spring |53 normally holds the piston retracted in its cylinder. This spring acts on a ring |54 xedly mounted on the piston rod |52 and there is a spacer sleeve |51. A washer |55 is mounted on'a sleeve |59 which is slidable on the urging the coupler to,-

rod and a spring |56 is Positioned between the t,

washer and the piston. The lever |35 has a pin |58 arranged to be engaged by the washer |55 at appropriate times as will presently appear in considering the operation of the mechanism. Associated with the piston is a valve actuating rod |60. This rod is capable of reciprocaton and is engaged by the piston in the latter stages of its movement caused by oil introduced in the cylinbecause the plunger |40 seats in the notch |152.`

For forward operation, the operator manually shifts the lever counter-clockwise so that the plunger acts on face |43 placing a load on the lever tending to shift the coupler in engagement` with the teeth 56. As explained above, a dental coupling will occur when the relative motion reaction of the coupler permits. As the speed of the vehicle increases to a certain value, oil under pressure is passed by means not shown into the cylinder |50 and the piston |5| is shifted to the left as Fig. 7 is viewed. The piston shifts rod |60 and the valve member 20| and the actuation of valve 20| introduces hydraulic medium into the clutch cylinder I3. Thus, Lthe clutch starts to engage and begins to transmit torque directly to the shaft |6. At the same time, the spring |56 has been loaded and it applies pressure to the lever |35 through pin |58 tending to withdraw the coupler from engagement with the teeth 56. As the clutch continues engagement and more and more torque is delivered to the shaft |6, the load on the teeth 56 and 51 is reduced to a point so near zero load that the energized spring rocks` the lever |35 clockwise and withdraws the coupler from engagement with the teeth 56. When this dental coupling is disestablished the clutch continues engaging and when fully engaged there is a direct drive through the clutch, through the shaft |6, and thro-ugh the iinal drive member I3. However, the lever |35 is not moved far enough clockwise to cause the notch |42 to be engaged by the plunger |40. n

If, for example, the vehicle drops in speed, oil under pressure is cut off from the cylinder |50 and the piston is moved back to the Fig. '1 posi-` tion by the spring |53. The rod |60 and valve member 20| are thus relieved by the piston and the hydraulic medium is cut oif from the clutch cylinder I3. The clutch starts to disengage and f the spring |4| and plunger |46 tends to swing the lever |35 counterclockwise to shift the coupler toward-engagement of its teeth 51 with the teeth 56 on gear 46. The relative motion reaction isv :8 such that vthe shoulder 16 engages theshoulder 14 as demonstrated inv Fig.1`10a and the coupler is blocked from further movement toward the gear 46 and the teeth 51 do notcome into engagement with teeth 55. However, as the engine continues acceleration with resultant acceleration of gear 45 the gear finally comes up to the speed of the coupler and the shaft and ultimately the blocking action is released. At this moment the teeth 56 and.51 are at substantially thesame speed and the coupler can move tothe left as Fig. 7 is viewed and dental engagement is established. If the operator shifts the lever |35 clockwise from the Fig. '1 position, the plungerengages face |44 and shifts the coupler to theright to engage teeth 58 and 59 for reverse drive'. i'

I claim:

l. In an automatic transmission for an automotive vehicle, a torque transmitting shaft, a torque ltransmitting member concentric with and rotatable relative to the shaft, a coupler slidably and drivably mounted on the shaft, the coupler 4and the member each having teeth for dental engagement and disengagement, a lever, a pivot for the lever, means connecting the lever to the coupler, the lever having a curved cam-like surface, a recess in said surface, a shoulder at one end of the surface and spaced from the recess, a spring pressed plunger operating on said surface between the recess and shoulder and placing aforce on the lever for moving it in a direction to urgethe coupler toward dental engagement with said member, said shoulder engaging the plunger when the coupler and member are in dental engagement, automatically acting re-v ciprocating fluid motor means operable in one stroke for shifting the lever in thev opposite direction to retract the coupler from dental engagement with said member, the maximum movement-provided by the fluid motor means being such that the recess is not moved into engagement with the plunger'whereby the coupler moves back into dental engagement with the said member upon operationof the fluid'motor means in its opposite'stroke,` and operator controlled means for moving the lever through an increment of movement greater than that imparted to it by said automatic means for engagement of the plunger with the recess to hold the coupler out of dental engagement with said member.

2. In an automatic transmission for an automotive vehicle, a torque transmitting shaft, a torque transmitting member concentric with and rotatable relative to the shaft, a second torque transmitting member concentric with and rotatable relative tothe shaft, a couple slidably and drivingly connected to the shaft and positioned between said two members, the coupler and each member having teethfor dental engagement, a lever, a pivot for the lever, means connecting thel lever to the coupler, said lever having a curved cam like surface with a recess in its intermediate portion, a spring pressed plunger engaging said surface, said plunger placing a force on the lever for shifting the coupler into dental engagement with one of said members, automatically acting reciprocating fluid motor means operable in one strokev for. shifting the lever in the opposite direction Vto retract the coupler from engagement with said one'member through a limited movement so that the said recess `does not comev into engagement with the f plunger whereby the coupler 'moves back into dental engagement with the said member upon' operation of the fluid motor means in its opposite stroke, manually controlled means for shifting the lever an additional increment in said opposite direction to bring the recess into alignment with the plunger so that the interengagement between the recess and plunger holds the coupler in a neutral position disengaged from both said members, said manual means being operative to shift the lever so that the plunger engages the said surface on the opposite side of the recess whereby the plunger places a force on the lever to shift the coupler toward dental engagement with the other of said members.

3. In an automatic transmission for an automotive vehicle, a torque transmitting shaft, a torque transmitting member concentric with and rotatable relative to the shaft, a second torque transmitting member concentric with and 1btatable relative to the shaft, a couple slidably and drivingly connected to the shaft and positioned between said two members, the coupler and each member having teeth for dental engagement, a lever, a pivot for the lever, means connecting the lever to the coupler, said lever having a curved cam like surface with a recess in its intermediate portion, a spring pressed plunger engaging said surface, said plunger placing a force on the lever for shifting the coupler into dental engagement with one of said members, automatically acting reciprocating fluid motor means operable in one stroke for shifting the lever in the opposite direction to retract the coupler from engagement with said one member through a limited movement so that the said recess does not come into engagement with the plunger whereby the coupler moves back into dental engagement with the said member upon operation of the fluid motor means in its opposite stroke, manually controlled means for shifting the lever an additional increment in said opposite direction to bring the recess into alignment with the plunger so that the interengagement between the recess and plunger holds the coupler in a neutral position disengaged from both said members, said manual means being operative to shift the lever so that the plunger engages the said surface on the opposite side of the recess whereby the plunger places a force on the lever to shift the coupler toward dental engagement with the other of said members, and an abutment at each end of said surface on the lever for engaging the 10 plunger when the coupler is in dental engagement with the respective members.

4. In an automatic transmission for an automotive vehicle, a torque transmitting shaft, a torque transmitting member concentric with the shaft, a coupler slidably and drivably mounted on the shaft, the coupler andA member each having teeth for dental engagement and disengagement, a lever, a pivot for the lever, means connecting the lever to the coupler, said lever having a cam face and a dentent portion, a spring pressed plunger engageable with the detent portion to hold the lever xed in position with the coupler disengaged from the member, manually operable means to shift the lever to cause the plunger to act on the cam face whereby to tend to turn the lever and shift the coupler towards dental engagement with said member, a cylinder for receiving hydraulic medium, a piston in the cylinder having a rod projecting therefrom, a sleeve slida'ble on the rod, a spring between the piston and the sleeve, and means on the sleeve for engaging the lever to swing the lever in a. direction for withdrawing the coupler from dental engagement with said member, the effective stroke of the piston being less than that required to shift the lever to a position of engagement of the detent means and the plunger.

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